Antenna system



Wm; 22, W42. A. ALFORD 2,305,113

' ANTENNA SYSTEM Original Filed April 26, 1939 6 Sheets-Sheet 2 I 7 *wzZ 1108 INVENTOR AMP/Z674 flL F061 ATTORNEY D R O F L A A ,wam

ANTENiqA SYSTEM Original Filed April 26, 19:59

6 Sheets-Sheet 3 y INVENTOR AMI/P0674 ALFORD Y EM/W ATTO R N EY A. ALFORD 23%,1 1 3 ANTENNA SYSTEM Original Fiied April 26, 1939 6 Sheets-Sheet 4 INVENTOR M .1503 IVA 056W fll/"UFD rim/17w 1505 BY W 1604 ATTORNEY mm. 22, mm. A, ALFQRD 2,306,113

ANTENNA SYSTEM Original Filed April 26, 19 39 6 Sheets-Sheet 5 ATTORNEY A. ALFORD ANTENNA SYSTEM Original Filed April 26, 1939 A l? 172a 6 Sheets-Sheet 6 \NVENTOR fill 095W I74 FORD BYW ATTORNEY Patented Dec. 22, 1942 ANTENNA SYSTEM Andrew Alford, New York, N. Y., assignor, by mesne assignments, to Federal Telephone and Radio Corporation, a co Original application A rporation of Delaware pril 26, 1939, Serial No.

1941, Serial No. 403,519

9 Claims. (01. 25011) This is a division of application Serial No. 270,173, filed April 26, 1939, Patent No. 2,283,897, dated May 26, 1942, entitled Antenna systems.

My invention relates to antenna systems particularly for use with plane polarized waves.

There appears to be considerable evidence favoring the use of directional and guiding systems using horizontally polarized waves for guiding aircraft in the horizontal plane.

A number of different kinds of radiators have been tried experimentally but it has been demonstrated that none of these radiators operates to radiate exclusively horizontally polarized waves. In order that this point may be made more clear, reference is made hereinafter to experiments which have been conducted with course beacon antenna systems. For this experiment the radiator consisted of two horizontal half-wave dipoles crossed, that is, arranged at right angles to each other.

Since the electric field around any linear radiator always points toward the radiator, it is clear that at any point lying above the plane of the two crossed half-wave radiators used, the electric fields at a point above the radiator and a distance away therefrom in a horizontal direction, due to the individual radiators, are not horizontal but are inclined to the horizontal by an amount dependent upon the elevation of the point above the radiator and horizontal distance that it is spaced therefrom. For this reason if a pick-up antenna carried on an airplane be inclined at some angle to the horizontal in a direction transverse to the course of the airplane, the ratio of signals from the two crossed radiators will be changed and the course or apparent plane of equality will shift. These effects of shifting the course due to imperfections in the horizontal radiation were observed during the experiments above mentioned. This effect is of considerable magnitude when the airplane is located at a large vertical angle with respect to the radiator.

When vertically polarized radiators are used this elfect is not observed because with the vertically polarized radiators the field is vertical at all points, so that any deformation of the receiving antenna on the airplane will only decrease the magnitude of the received signal but will not decrease the signal from one radiator with respect to the other so as to produce a false or shifted course.

This problem is probably more serious than is at present appreciated because of the possibility that the airplane receiving antenna may be injured during take-off or by sleet, or may simply 55 now Patent No. 2,283,897, dated May Divided and this application July 22,

be out of proper adjustment and thus produce entirely erroneous indications because of the presence of the vertical as well as the horizontally polarized components of the waves.

There is also another possibility which, so far as I am aware, has not at all been appreciated, namely, that parts of the airplane will pick up the vertically polarized waves and then re-radiate them to the supposedly horizontally polarized receiving antenna. Since each airplane itself may be different in structure, these errors will be inherent in each type of airplane and will be difierent for each diiferent airplane. This error will also be diiferent for difierent vertical angles and therefore is not subject to simple compensation. Since such errors will cause different course indications for different airplanes in the field of the same beacon, it is quite obvious that the situation would be intolerable because it would necessitate the individual investigations of each airplane.

All of these difierent difiiculties, as well as some others not specifically enumerated would be eliminated if the electric field of the beacon or iocanzer antenna giving the course indication were made horizontal at all points. may be accomplished by an antenna system constructed in accordance with my invention, Ior producing only plane polarized waves. Such an antenna system for producing Only plane polarized waves is likewise readily applicable ior stationary receiving systems and will result in a receiving arrangement superior to those now in use since it Will be more completely selective to reception of plane polarized waves.

According to my invention I have devised an antenna system which substantially eliminates all of the vertically polarized wave components of a received or transmitted wave. This is accomplished by dimensioning the antenna and so energizing it that the vertically polarized components of a wave will be substantiaily neutralized in every direction from the antenna.

The provision of such a plane polarizing antenna is one of the principal objects of my invention.

A further object of my invention is to provide a radiating or receiving antenna which will have a radiant action substantially only for plane polarized waves forming substantially a circular radiation pattern in the plane of polarization.

It is a still further object of my invention to provide a receiving system for plane polarized waves utilizing a receiving antenna subject to reception of only waves polarized in the plane of the antenna.

It is a still further object of my invention to provide a radio beacon built up of antenna units radiating only horizontally polarized waves.

Other objects and advantages of my invention will be apparent from the particular description thereof made in connection with the accompanying drawings illustrating a few of the embodiments of my invention, in which Fig. 1 illustrates in plan view one form of an antenna constituting an embodiment in accordance with the principles of my invention;

Fig. 2 illustrates in plan. view one form of constructive arrangement of the antenna of Fig. 1;

Fig. 3 illustrates in plan view a modification of the antenna arrangement of Fig. 1 utilizing only one loop conductor;

Fig. 4 illustrates a modified antenna structure embodying the principles of my invention;

Figs. 5 and 6 show a plan view and elevational view, respectively, of a practical constructive embodiment of the antenna illustrated in Fig. 4;

Fig. 7 illustrates a further practical embodiment of the antenna of Fig. 4 arranged in circular form;

Figs. 8 and 8A illustrate still further embodiments of my invention utilizing the principles outlined above;

Fig. 9 illustrates a vertical cross-sectional of the field pattern radiated or received by the antenna system in accordance with the principles of my invention;

Fig. 10 is a diagrammatic illustration used to explain the cancellation of waves polarized in planes other than that of the antenna;

Fig. 11 illustrates a receiving circuit utilizing an antenna in accordance with my invention designed for the reception of more than one frequency;

Fig. 12 illustrates a modified form of the antenna according to Fig. 11, utilizing condensers for improving the operation of the antenna;

Fig. 13 illustrates a practical constructive arrangement of the condenser shown in Fig. 12;

Fig. 14 illustrates an array arrangement of antennae constructed in accordance with the principles of my invention;

Fig. 15 illustrates a beacon transmitter system in accordance with my invention and using antennae of the type disclosed above and a coupling system permitting the simultaneous production of angularly related radiation patterns;

Fig. 16 illustrates the field pattern radiation diagram for an antenna beacon such as shown in Fig. 15;

Fig. 17 shows another form of beacon in accordance with my invention;

Fig. 18 shows the field pattern from the beacon of Fig. 17; and

Figs. 19 and 20 show views of an antenna structure particularly suited for beacon use.

Turning first to Fig. l, I have shown an arrangement utilizing an antenna indicated generally at 48 coupled to a high frequency source or load 4|.

In Fig. 1, an embodiment of an antenna in accordance with my invention is disclosed. In this figure the antenna '39 is shown coupled to a high frequency source or load ii. The antenna is composed of two conductors comprising sections 42, 33, M, 45, t6 and t2, 13, M, and 56', re spectively. The conductors are open circuitecl and are made electrically a half-wave long so that at the ends of the system will occur current nodes.

Parts of each conductor, namely, 42, 48, and 42, 46 are arranged close to each other and at the ends of conductors E2, 42 is coupled a high frequency translator which may constitute a source of energy or a load. Sections 42, 42 and 46, 46' are preferably chosen of such length that the current maximum occurs at the center of the radiating portion of the conductors, namely, at the mid-point of conductors 4 1, M, and the radiating sections comprising portions of the conductors 43, 44, and 43, 44, 45', are made short relative to the operating wavelength so that a substantially uniform current distribution is obtained. These radiating sections are made prefferably of a length in the order of 1 6 to /a of a wavelength, but should in any case not exceed /3 of a wavelength, while the total overall length of each conductor is preferably /2 a wavelength electrically.

The energy source 4! should be connected to energize the conductors in phase opposition so that the instantaneous direction of current flow is around the periphery in the same direction in the radiant acting elements, and is opposite in the closely spaced conductors. In case ll is a receiver the receiver is coupled at the same point as would be required for an energy source, in order to obtain the same operation. It is well known that in any antenna system a receiver must be coupled at a point such that if it were replaced by a source the desired characteristics would be obtained. For this reason the connection of the translating device is made in terms of the effect of a source at this point because no other simple generic language is available.

In the illustration of Fig. l, the two radiant acting portions are shown each substantially /6 of a wavelength long. The current distribution will then be substantially as indicated by the shaded portions Mat-45a and Mb. It will be noted that in M, M; 3, 45; and 43', 45'; the current distribution is equal so that at any point from the midpoints of these lines complete neutralization of vertical polarization may be achieved. The currents in the arms 44, and 43, 43', are not quite equal but are of the same order of magnitude and consequently substantial neutralization will occur at angles to the loop sides. A more complete explanation of this neutralization will be made later in connection with Fig. 10. This arrangement of antenna is particularly advantageous for use on portable receivers, since the antenna itself may be made very small still preserving a fair eificiency and a high degree of discrimination against waves not polarized in the plane of the antenna.

In Fig. 2 is illustrated an antenna 56 in accordance with a practical structural arrangement of the antenna shown in Fig. 1. In this arrangement leads 56, are bent downwardly and are enclosed in a grounded shield 57, and the feeders 52, 52', are also enclosed in a grounded shield 58. This construction prevents radiation from these portions of the system so that no Vertically polarized waves will result therefrom. Because of the parallel capacity effect of the shield, conductors 56, 56 are considerably shorter in physical length to obtain the devised electrical length, than if no shielding is present.

In Fig. 3 is shown a modification of the arrangement illustrated in Figs. 1 and 2 utilizing a single leg of the loop, the other leg being constituted by the image conductors in the conductive surface. In this arrangement a high frequency source Si is coupled over a shielded conductor 62 to the radiating loop 63, the end of the conductor being constituted by shielded open ended conductor 64. The dimensions of the single conductor of this modified loop are prefer-ably made the same as those illustrated in connection with a single conductor of Fig. 1. As a consequence the radiation pattern of the antenna of Fig. 3 is substantially similar to that produced by the structure illustrated in Figs. 1 and 2.

In Fig. 4 is illustrated a further embodiment of my invention utilizin four different radiating conductors instead of two as in the other embodiment. This structure is especially adapted for use as a radiating antenna, since with the four conductors a larger radiation resistance and a consequent increase in energy radiation may be obtained. It is clear, however, that this antenna may also be utilized for reception, since it also provides an increased amount of pick-up.

In Fig. 4 is provided a high frequency source coupled over conductors l, 2 to four radiators I3, 14, 75 and 16. High frequency source 10 is preferably connected to the mid-point of conductors H, H and the electrical length from the point of connection to the radiating conductors l3. l6 and to the ends thereof as shown at l3, I6 is made electrically equal to an integral half-wave length of the operatin frequency. Conductors l3, l4, l5 and 16 are arranged in a square and the end of each radiator is bent inwardly as shown at l3, l4, l5, 16, so that only the central portions of the conductors are utilized for radiation. Radiators 13 and 16 are fed directly from high frequency source over conductors ll, 72, and radiators M, 15 are fed over conductors 12, H to a means for producing a 180 phase shift such as the transposition shown at 11. As a consequence the currents fiow through the conductors in the direction indicated by the arrows, the current disposition in each of the four radiators is uniform, as indicated by the solid shaded area Ltd to 16a. Each radiating section is preferably made short with respect to the operating wave length so that the current distribution is high throughout the length thereof, and since the current distribution is equal in each of the four arms, and is opposite in phase on the opposite sides thereof, the vertical field component will be substantially eliminated in every direction and for every vertical angle with respect to this radiator. Furthermore, since substantially uniform current distribution is provided in the radiator the resulting radiation pattern will be substantially circular.

An embodiment of the antenna in accordance with the principles set forth in connection with Fig. l, is illustrated in Figs. 5 and 6. In this arrangement the radiators consist of four members 8M, B62, 803 and 804. These members may be comprised of hollow tubular conductor if desired to decrease the weight. Each of these radiators extends through entrance type insulators 805 into metallic shielding boxes designated as 806. Tubular metallic shielding members 801 extend downwardly and inwardly to metallic shielding box 308 from the lower end of which extends the shield 839. The energy feeding leads of the antenna 8N) extend downwardly from diagonal corners of the antenna to the metallic tube 801 into the shielding box 808 where the transposition is made and any necessary impedance matching of the antenna to the feed supply leads 813, is made. The other or reentrant end of the radiators 8| I, 8| 2 extend downwardly in the opposite diagonally arranged shielding tube 801 and so are completely shielded. With this arrangement only the parts of the whole radiating structure containing the current loops are exposed to the weather. The insulators 805 at the end of the radiators are near voltage nodes of the system, so that no high voltage strength existed thereacross. The entire supporting frame is arranged beneath the radiating structure and inside the patterns thereof so that no part of the supporting frame is in the field of the radiators. The radiation resistance of this structure is high in comparison with the resistance of the wires or insulators so that a very high efficiency is obtained.

In an actual demonstration of an arrangement in accordance with this construction, it was found that the radiation pattern was substantially circular in the horizontal plane.

The radiator of the system according to my invention may be of shape other than straight conductors. In Fig. 7 is illustrated an arrangement similar to that shown in Figs. 5 and 6, except that the radiators are each curved so as to form substantially a circular pattern when assembled. Similar reference characters are used in Fig. 7 to designate the various elements corresponding to those shown in Figs. 5 and 6.

The radiating system may be composed of more than four conductors, for example, it may comprise eight units arranged in the form illustrated in Fig. 8. In this figure the high frequency load or source H00 is coupled to a pair of transposed conductors lllll. These conductors are connected to radiators H02, H03, H04 and H05. Other radiating conductors Hill, H08, H09 and HID are arranged as shown in Fig. 8. In each of these conductors the terminating ends are bent inwardly as shown and arranged close thereto. This arrangement of the terminating ends of these radiators provides a coupling between the directly energized antennae elements H02, H03, H04 and H05, so that each of the other sections Hill to HID, inclusive, are also energized. Thus is provided a radiating antenna for radiating only horizontally or other plane polarized waves into which a high radiation resistance may be obtained and consequently a greater efiiciency of operation.

Instead of using the inturned ends of conductors for coupling together the sections as shown in Fig. 8, condensers may be used as shown at H00, Fig. 8A. In this case it may be more convenient to mak the condensers in the form of strain insulators and the radiant acting sections may be bent in their centers for fastening to a support.

In Fig. 9 is illustrated a vertical section to the radiation pattern produced by antennae in accordance with my invention. The horizontal axis is designated by HE and the vertical axis by VV. The field is represented by the tangent curves F, F. The field is actually in the form of a lemniscate similar in pattern to that obtained from the radiation of a single dipole, but differs therefrom in that there are no vertically polarized components. The voltage at any point in the field may be expressed by equation E=Eo cos 0 where E0 is the voltage in the horizontal frame and 0 indicates the angle of elevation.

The radiation resistance for antennae in accordance with my invention wherein the current distribution throughout the arms is substantially uniform may be expressed by the equation ohms R 320 ohms where l is the length of one of the radiators in the same units as the wavelength A. A preferred range or" radiation resistance is between 7 and ohms.

A more complete explanation of the operation of the antenna in accordance with the principles of my invention may be obtained by reference to Fig. 10, showing a three dimensional view of a quadrant of the radiation field from a radiator similar to that illustrated in Fig. 4. The arms corresponding to the four radiators of the antenna are designated by letters A, B, C and D, as shown, with arms A and C being opposite each other and arms B and D being arranged opposite to each other. The intersection of the planes are designated by the heavy lines X, Y and Z, the horizontal plane being the X, Y plane, the two vertical planes being the Z, Y and Z, X planes, these planes being bounded by curves XY, ZY and ZX, respectively. A third plane is passed through the diagonal of the radiator represented by the lines Z and 9 W, and bounded by the curve w. At any point P on the line w, making a vertical angle with the plane of the radiator, can be assumed to be a receiving point. The dot-dash line starting at X and extending through point P, repre sents the meridian of polarization of energy from radiators A and C, and the broken line extending from Y through point P, represents the meridian of polarization from radiators B and D. At point P the radiation from radiator C will have a large horizontal component and a small vertical component as shown at c, and at the same time the radiator D will produce a horizontal component in the same direction as that from C and a small equal vertical component oppositely phased to that of point C. It is therefore clear that these two vertical components being equal and opposite will cancel, since P is equi-distant from both radiators B and D. Similarly at point P the vertical components from radiators A and. B will cancel as shown at a, b, and the horizontally polarized compcnents will add together in phase although they are of opposite phase from elements C and I). Since radiators A and B are at different distances from point P than radiators C and D, there will be a horizontally polarized component which can be received. The vertically polarized components, however, are completely cancelled as explained.

At points P1 still at the same vertical angle it can be seen that the radiation from elements from radiators B and D, will be largely vertical but wiil be in opposite directions. Since point P1 is equi-distant from radiators B, D, the vertically polarized waves will therefore be cancelled at this point. The horizontally polarized waves at point P1, arriving from radiators A and C, are of opposite phase but since they come from difierent distances, 2. horizontal component will be present for reception. Similarly at point P2 the horizontally polarized component from B and D will be received, whereas the vertically polarized component from A and C will be neutralized. If the vertical angle at which P is located is varied, the same effect will occur, since as shown, P represents a point at any vertical angle. Similarly, since the points chosen for illustration represent the extremes in so far as the radiator is concerned, it is clear that the vertically polarized components will be neutralized everywhere about the loop regardless of the horizontal angle.

In planes intermediate the and 45 degree position discussed in detail above, for example, in. a plane nearer the X axis, the vertically polarized components from B and D increase but will approach equality in opposite phases. The vertically polarized components from A and C will also approach equality in opposite phase. As a result the sum of the vertically polarized components at this intermediate point will be such that the components from A plus the components from D is equal in magnitude but opposite in phase to the vertically polarized components from B plus the corresponding component from C. Accordingly, it is seen that the vertically polarized components will neutralize in every direction about the antenna. Careful test measurements of vertical components about such an antenna verify this conclusion.

This explanation has been made with reference to the four armed loop such as shown in Fig. I. It is clear that the same principles apply in varying degrees to the other arrangements such as those shown in Figs. 1, etc.

In the arrangements as shown in Fig. 1 the neutralization, however, will not be as complete in all directions because there is not a complete equality of currents in the loop sections. For example, turning to Fig. 1, it is clear that the current in M, for example, is not exactly equal to the sum of the currents in 45 and 45' and for this reason a complete neutralization of the vertical components will not be present. However, a close approximation of complete compensation may be achieved by use of this loop.

In Fig. 11 is illustrated an installation of a loop according to my invention, for use as a receiver. This loop is designed for receiving two diiierent frequencies and for this reason is somewhat of a compromise in design. In this installation the two radiators I 30! and I382 were arranged to form an oval loop approximately 17 long and 10" on the minor axis. The two frequencies f1, f2 for which the circuit was designed, are 93 and 109 megacycles, respectively. The receivers are represented at I303, I304 in the drawing. A metal plate NW5 mounted on an insulating handle I386 is provided for Vernier tuning of the circuit. The radiators are coupled over a special loaded line will across two shielded conductors I 308, I 30d. Section I3fi8 is made equal to one-half of the wavelength m, for which receiver I304 is designed. Thus the line is rendered tuned to f2 so that any addition at the termination of line I301 will not affect the line substantially for energy of )2. I354 is inductively coupled to line I308 by a tuned coupling so that energy other than that for which it is designed will not be received. Receiver I3Ei3 tuned to I1 is coupled over a shielded pair symmetrically to the antenna over I3lil and ISM. The metal shields around line sections I308, I 309 are conductively joined together. The

line I301 is made by means of a special loading approximately a quarter of a wavelength long electrically although the actual length is much shorter. In the installation the actual length of line I301 was approximately 11'. A concentric line I3I0 is used to connect transmission line section I308 to receiver I304, and a shielded pair transmission line I 3 is used to couple section I300 to receiver I303. In the installation actually made the shields about line sections I300, I308 were made of concentric tubular conductors of outer diameter and the concentric transmission sections I3I0, I3II were made of concentric transmission lines of one-quarter inch outer diameter.

The loaded line I301 has a relatively high value of surge impedance. This extra high value of surge impedance was found desirable in order to reduce the circulating current in the half-wave length line. The impedance of the loop itself at the upper terminals may be very high, for example, say the value is R. Then the impedance at the bottom of the special section line I301 is where Z is the surge impedance of the line. When Z0 has a low value, impedance r is very low and consequently there is a large current flowing 4 four coils of about twelve turns each, with an I outer diameter of about a quarter of an inch, spaced a half an inch apart the total loss was reduced to one decibel. In order to complete the shielding, screening boxes I3I0, I3I5, may be provided.

A further modification by way of improvement of the antenna shown in Fig. 11 is illustrated in Fig. 12. In the loop installation such as shown in Fig. 11, a considerable voltage exists in the loop at the ends of the loop where it is supported by its insulators. The consequent high impedance at the insulators leads to two troubles. (l) The tuning of the loop is relatively sensitive to additions of capacity, for example, snow may produce a effect, and (2) the high impedance of the insulator requires the use of such a loaded line to reduce loss in the two frequency, tuning circuit illustrated.

Even with the specially loaded line it may still be necessary to use fairly large concentric tubing for the half-wave line section to reduce losses to a reasonable value. The use of a lighter concentric line, for instance, a quarter-inch line would be preferable because of the ease in bending and lighter weight.

In order to improve the operational characteristics in so far as this voltage distribution is concerned, the loops may be constructed in accordance with the showing of Fig. 12. In this arrangement each of the arms I i-0i, I402, are broken up by means of condensers M03. The voltage distribution about the loop becomes about in the form represented at V. At the same time the current distribution in these parts of the conductors is approximately as represented at I0 in the lower half of Fig. 12. Considering the surge impedance of the loop conductors as Z0, and the distance between two consecutive condensers as 20, then V=Zo0 sin 6.10. Where I0 is the low loop current which occurs half-way between the condensers; the general current i=Iu cos 0; the capacity C of a condenser is determined from the following formula l/cw=2Zu tan 0 where 7 (1:21 frequency For example when F m. c. Z0=500 ohms that is 26 about 6", then 1012 6.28 X 10 X 10 X176 It is seen that the capacity C of condenser I403 is very small. This capacity may be obtained by a very simple fitting such as illustrated in Fig. 13. In this arrangement the conductor forming the radiators I50 I, I502, may be a metal tube, for example, aluminum tubing. Into the ends of these tubes is inserted an insulator I503, which may be a ceramic tube. Through the tube is inserted a metallic rod I504 provided with enlarged ends I505, I500, which will serve as the seats of capacity for the condenser. Tube I 504 may also be of aluminum. The two conductors I50I, I502 are then clamped in position on insulator I503, by means of clamping rings I506, I507.

By replacing the loop shown in Fig. 11 by a loop provided with condenser such as shown in Figs. 12 and 13, the voltage at the insulators would be reduced to about one-third of the value without the condensers and the impedance would be reduced to about one-ninth of the value obtained otherwise. It is clear that with this type of loop, the circuit will be much less sensitive to capacity changes such as caused by snow or ice, and furthermore the loss in tuning the circuit will be considerably reduced.

Because of the substantially complete absence of vertically polarized components the antennae in accordance with my invention are particularly suitable for use as horizontally polarized guiding beacons or runway localizer beacons, since they will not produce faulty shifting of courses due to variations in polarization at vertical an les. One form of radio beacon arrangement utilizing antennae in accordance with my invention is illustrated in connection with Figs. 14 to 16. i

In Fig. 14 two antennae I 0M and I0 2 are shown, preferably mounted a half a wavelen th of the operating frequency apart. These antennae are preferably of the t e illustrated in Figs. 5 and 6, but may be of any of the other tvn s illustrated in the application. Antennae I'A II and I002 are connected together over a transmission line I603. Coupled to the tran mission line I603 is high frequency ap aratus IBM connected by means of line section I 505 midway between antennae IBM and I602. A 180 phase shift is provided, for example by a transposition provided in line I603 at I000. Thus antennae I60I, I602 are located a half-wavelength apart and are energized in phase opposition. This energization of the loops in phase opposition produces a radiation pattern having a null point midway between the two antennae, as shown in Fig. 16 at F1. If the transposition I 600 is omitted, then antennae IBOI,

I602 will be energized in phase. This will produce a radiation pattern having a null in the direction of the extension of the antennae, as illustrated at F2, in Fig. 16. These variations in radiation pattern may be produced by any suitable keying means for alternately transposing the line.

In Fig. 15 is illustrated an arrangement for producing a guiding course by simultaneous energization of two antennae spaced a half-wavelength apart. The antennae I10I, I102 are connected over transmission lines I103, I100, to opposite corners of a balanced network indicated generally at I104. This network is preferably made of open lines and i provided with two sets a of arms I105, I106, a transposition is arranged in arms I105. Because of this transposition energy introduced or withdrawn at any corner of the network will have no effect on the apparatus connected diagonally opposite therefrom as long as the impedances are balanced, although it may effect any apparatus connected to the other corners. A transmitter which may be a common high frequency source I1 I is provided, from which is derived two separate signalling energies which may be differently modulated with frequencies F1, F2. The energy thus modulated is transmitted from the separate transmitter output I1II, I1I2. Energy from H modulated at F1 is applied to one corner of the bridge I100, so that radiators II, I102, are energized over the transposed section and thus radiate the pattern F1 of Fig. 16.

Simultaneously the energy from I112 i applied to the diagonally opposite corner of the network I104 so as to feed antennae I10I, I102 in phase. Thus there results a pattern such as shown at F2 of Fig. 16.

The four arms of bridge I104 are preferably in length eoual so that at point 1) looking in from a, the effect is the same as though a short circuit existed at, this point. However. arm I105, I108, and I106. I101 may not present an impedance match with respect to energy entering from point a. and reflections from b. will result. Similarly ener y from point 1) will be reflected at a. By

properly dimensioning the arms the lengths may be so chosen that the reflected energy will just compensate for the mismatch and the circuit will operate so as to prevent reflections on the feeding lines. I have discovered that in order to provide .3

for this effect the individual arms of the bridge network should be substantially .15 of a wavelength long at the operating freuuency.

As shown in Fig. 16 the radiation patterns are not circular but are deformed so that pattern F1 a.

is somewhat flattened and F2 is elongated. The courses are consequently at an angle less than 90 as in the case of circular radiation atterns. The courses actually extend at about 60 with respect to one another. There is provided a beacon arrangement for forming four separate guiding lines towards the beacon. Since the antennae units also are provided to cause substantial neutralization of the vertical field component. the

beacon si nals will be derived solely from hori- :7

zontally polarized waves. Thus any receiver coupled to this system will operate to give the proper course. regardless of any variation in the polarization of the receiving antennae.

In Fi 17 is il ustrated another form of beacon part cu arly useful for the utilizing antennae in accordance with the principles outlined above. In this figure high frequency source I1I0 is coupled to two modulators Ill! and I1I2 and to a bridge network I100, similarly to the arrangement illustrated in Fig. 15. The arms of the bridge network are preferably made .15 of a wavelength long as explained in connection with Fig. 15. However, instead of only two antennae, four antenna units I12I and I are provided. Units 1121 and I124 are connected together by transmission line I125 in which is provided the phase reversal means, such as the transposition I125, so that they are energized in phase opposition. Line I125 is connected to one corner of bridge I104 by line I121, at a point electrically midway between I12I and I120. Two other antennae I122, I123 are connected together by a transmission line I120 which is connected. by means of a line I129 to the corner of bridge i100 diagonally opposite the point of connection of I121. Line I129 is made 90 shorter electrically than I121 so that these units are energized in phase quadrature with respect to units l12I and I124.

The energy supplied from modulator I1II modulated at frequency )1 then energizes antennae I12I, I124 at 180 phase difference, as indicated in the drawing, and simultaneously energizes antenna 1122, I123, in phase with energy at -90 phase displacement with respect to energy supplied to the other two antennae. Similarly, energy from I1I2 modulated at 12 energizes antennae E12I, I124 at 180 phase difference but also at 180 out of phase with energy 11H. The antennae I12I, I124 are displaced a distance a from the center line of the array an antennae I122, I123 are spaced apart a distance ,6. The radiation pattern from these arrays will then be formed somewhat as shown in Fig. 18. In this figure the broken line curve Fi respresents the transmission pattern from modulator HI I, and the solid line curve Fz represents the energy transmitted from I1I2. The modulator I1II may be provided to furnish a modulation frequency, for example, 170 cycles, and modulator I1I2 a modulation of different frequency, for example, 90 cycles, so that the signal equality course may be readily determined on a craft.- Both patterns F'i, F'2 have some minor lobes of radiation but these are of such small amplitude as to be neglected with respect to the main guiding part.

The spacing between the antennae may be varied to change the shape of the radiation pattern. However, a preferred form using a spacing in which a equals 170 electrical degrees, and 5 is made equal to electrical degrees, produces a very sharp pattern free from bothersome minor lobes of radiation.

For use as radio beacons, the structure shown Figs. 5 and 6, presents some difficulties since the shielding arrangements such as 801, are at an angle to the vertical and are also disposed in the radiation field of the other antenna unit. For this reason these angularly disposed sections will pick-up and reradiate some energy and for this reason interfere with the pure horizontal polarization. In order to overcome this difficulty the antennae may be constructed in the manner shown in Figs. 19 and 20 so that substantially no vertically polarized radiation will be produced.

In Fig. 19 a front view of this antenna is shown with the cover of central boxes removed so as to show the construction. According to this arrangement, two hollow metal boxes I90I, I202 are provided. To the other side of each of these boxes is fastened a concentric cable arrangement I903, I900, the center conductor of which may be used to feed the antennae. In the sides of boxes IBIJI, I902, at the point where they are adjacent each other, a hole is provided so that a transposition of the feeding conductors may be achieved. These conductors I995, Iiitfi are led through suitable shields to the radiant acting conductors IBM to ISM, inclusive. Conductors IQII to IBM are preferably made heavy and may be as shown, made of strips of metal, such as copper. ments of large dimensions, the resistance thereof is greatly decreased. This is of importance since by decreasing the surge impedance of the radiators themselves, considerable reduction of the voltage across the insulators connecting conductors I936, I985, may be achieved. The inturned end of the conductors I9 to I 9I4, are supported by means of a plate Hill and may be covered by suitable weatherproof covering l9l8. By this arrangement all of the angularly related conductor portions are obviated, and consequently harmful vertically polarized radiations are averted.

It should be noted that the beacon arrangements disclosed herein are well suited for producing radiation beacon patterns. It is further noted that the spacing between the antennae units is such that radiators of a half wavelength could not be used. Therefore, the particular antennae units in accordance with my invention are admirably suited for this purpose. It should be understood, however, that the particular balancing arrangement and the beacon system may be utilized also, with other forms of antennae, than those producing horizontal polarization While I have illustrated a few preferred embodiments of my invention, it should be distinctly understood that this description is made merely by way of illustration and is not intended as a limitation on the scope of my invention. What I intend to cover as my invention is defined in the accompanying claims.

What I claim is:

1. A radio beacon system for operatingat a given frequency comprising a pair of spaced radiating means, a first energy source for producing waves of said operating frequency characterized by a particular signal, a second source of energy for producing waves of said operating frequency characterized by a second signal and means for supplying energy from said first source to said radiating means in one phase relation, and from said second source in a different phase relation, comprising a two conductor four arm reentrant bridge network having a 180 phase shifting means in one arm thereof, coupling means coupling diagonal junction points of said arms to said radiating means, means coupling said first source of energy to said bridge at the junction point of said arm provided with said phase shifting means and a second arm other than the radiating means coupling points. and means coupling said second energy source to said bridge at the junction point of said arms diagonally related to said last named junction, the arms of said bridge each being of substantially equal lengths, and so dimensioned with respect to the wavelength at said operating frequency as to produce reflections of energy from one source of such magnitude as to compensate for impedance mismatch of the system with respect to the energy coupling means of said source.

2. A radio beacon system according to claim 1,

By making these eledesigned to transmit wherein said radiating means comprising antennae units designed to transmit only horizontally polarized waves.

3. A radio beacon system according to claim 1, wherein each said radiating means comprise an antenna including a plurality of horizontal conductors arranged to outline a substantially closed periphery for radiating only horizontally polarized waves, said means being spaced apart substantially one-half a wave length at said operating frequency.

l. A radio beacon system according to claim 1, wherein each said radiating means comprises a group of at least two antennae, each including a plurality of horizontal conductors arranged to outline a substantially closed periphery, for radiating only horizontally polarized waves, the antennae 'of one of said groups being spaced apart a distance less than one-half a wave length at the operating frequency, and being arranged centrally with respect to the antennae of the other group.

5. A radio beacon system for operation at a given frequency comprising a pair of spaced radiating means, a first energy source for producing waves of said operating frequency characterized by a particular signal, a second source of energ for producing waves of said operating frequency characterized by a second signal and means for supplying energy from said first source to said radiating means in one phase relation, and from said second source in a different phase relation, comprising a two conductor four arm reentrant bridge network having a phase shifting means in one arm thereof, the arms of said bridge each being .15 of a wavelength long at said given frequency, coupling means coupling diagonal junction points of said arms to said radiating means, means coupling said first source of energy to said bridge at the junction point of said arm provided with said phase shifting means and a second arm other than the radiating means coupling points, and means, coupling said second energy source to said bridge at the junction point of said arms diagonally related to said last named junction.

6. A radio beacon system comprising a pair of antennae each designed to transmit substantially only horizontally polarized waves and spaced less than a half wavelength apart at the operating frequency, means for energizing said antennae in phase coincidence with energy of said operating frequency characterized by a particular signal and means for energizing said antennae in phase opposition with energy of said operating frequency characterized by a different signal, whereby four guiding courses are provided consisting only of horizontally polarized energy waves.

'7. A radio beacon comprising a first pair of antennae designed to transmit substantially only horizontally polarized waves and spaced apart a distance less than one-half wavelength at the operating frequency, a second pair of antennae substantially only horizontally polarized energy and spaced substantially equal distances on either side of said first pair of antennae, means for supplying energy characterized by a distinct signal to the antennae of said second pair of antennae in phase opposition, and to the antennae of said first pair in like phase and in phase quadrature with respect to said second group antennae, and means for su plying energy characterized by a diiferent signal to said antennae of said first and second pair in phase opposition to said first supplied energy, whereby a two guiding course consisting of only horizontally polarized energy is provided.

8. In a high frequency system, a first source of energy of a given frequency, a second source of energy of said given frequency, two load .circuits for said energy, and means for feeding energy from each of said sources to said loads in different phase relation, comprising a closed bridge network comprising four serially connected arms of substantially equal length, means in one of said arms for producing a 180 phase shift, means for coupling said first and second energy sources to diagonally opposed corners of said bridge network, and means for coupling said loads to the other diagonally related corners of said bridge, the arms of said bridge being so dimensioned as to produce a reflection of energy from said source just sufiicient to neutralize the efiect of the inherent mismatch of said network to said energy coupling means.

9. A high frequency system according to claim 8, wherein said arms of said bridge are substantially .15 of a wavelength long at said given frequency.

ANDREW ALFORD. 

